The concept of Top-Down Design has been around for a long time.  It is indeed a powerful method though it must be understood as a design paradigm not as a software module.

The truth is PTC did not invent Top-Down Design, and I think their use of the phrase is a marketing ploy with buzzwords.  Please don't misunderstand - the tools they provide are great - they provide some good methods for design efficiency - but be careful not to shoot yourself in the foot while you're at it.

This Tip-of-the-Month is a warning to users following the PTC Top-Down Design recipe with regards to assembly constraints.  From what I've seen, designers working along with the advertised Pro/E recipe need to be aware of constraints in their final assemblies.

Skeleton parts are a fantastic design tool for working with assemblies.  They are far more capable than most give them credit.  In the simple case demonstrated in our August 1998 tip, the crane parts are all assembled to the skeleton.  The function, placement and overall assembly is controlled with a few features of the skeleton.  This is fantastic, especially in the concept phase.  However, there comes a time when the skeleton control should be reduced or eliminated.

The functional constraints like Mate, Align, Insert, Edge on Surface, etc. from parts to parts have real meaning.  As the assembly matures through the design process, it should reflect more and more reality, which includes the methods of assembly.  True, this takes a bit more effort, but an assembly constructed primarily using the skeleton and other "non-functional" constraints can result in an assembly that will not work in reality - which is a bad thing for career advancement.

Use the tools Pro/Engineer provides, but understand the limitations.  One of my favorite quotes:   "When the only tool you have is a hammer, everything begins to look like a nail."